Preexisting Software Checking

The installer examines the computer on which you are installing and identifies
the Java ES components that are already installed. The installer then checks
at several levels to make sure that all existing components are at the appropriate
release level to interoperate successfully. The installer informs you about those
software components that are incompatible and must be upgraded or removed.

Similarly, the installer checks for Java ES shared components (see Shared Components), such as J2SE or NSS, that are already
installed. If the installer finds versions of shared components that are incompatible,
it lists them. If you proceed with installation, the installer automatically upgrades
the shared components to newer versions.